linux-kernel - Re: [PATCH [RT] 05/14] rearrange rt_spin

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Message-ID: <20080222133541.GA8868@elte.hu>
Date:	Fri, 22 Feb 2008 14:35:41 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	gregory.haskins@...il.com
Cc:	Gregory Haskins <ghaskins@...ell.com>, a.p.zijlstra@...llo.nl,
	tglx@...utronix.de, rostedt@...dmis.org,
	linux-rt-users@...r.kernel.org, linux-kernel@...r.kernel.org,
	bill.huey@...il.com, kevin@...man.org, cminyard@...sta.com,
	dsingleton@...sta.com, dwalker@...sta.com, npiggin@...e.de,
	dsaxena@...xity.net, ak@...e.de, gregkh@...e.de,
	sdietrich@...ell.com, pmorreale@...ell.com, mkohari@...ell.com
Subject: Re: [PATCH [RT] 05/14] rearrange rt_spin_lock sleep


* Gregory Haskins <gregory.haskins.ml@...il.com> wrote:

> My assumption is that the xchg() (inside update_current()) acts as an 
> effective wmb().  If xchg() does not have this property, then this 
> code is broken and patch 6/14 should also add a:

xchg() is a strong implicit memory barrier, it implies smp_mb(). 
(historic sidenote: it was the very first SMP primitive we had in 
Linux.)

	Ingo
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